The invention relates to photochromic plastic objects, which contain a specific combination of at least two pyran derivatives, each substituted with a group containing nitrogen, particularly with an amino group or with a heterocyclic nitrogen group, and which are distinguished particularly by a long service life, a good decolorization rate, the absence of yellowing as well as by a neutral perceived color, it being possible to dispense largely or completely with the use of stabilizers and the like in the inventive plastic objects. The invention furthermore relates to the use of said photochromic plastic objects.
Different classes of dyes are known which, when irradiated with light of a particular wavelength, especially with sunlight, change their color reversibly. This is due to the fact that, because energy is supplied in the form of light, these dye molecules change over into a stimulated colored state, which they leave once again when the supply of energy is interrupted in order to return to their colorless or at least hardly colored normal state. These photochromic dyes have recently been used increasingly in various ways in plastic products.
Photochromic plastic products, especially eyeglass lenses, have been obtainable commercially since the early 1960s. The first lenses, which were disseminated increasingly were, for example, Rodenstock Perfalit Colormatic.RTM. (Trademark of the Optischen Werke G. Rodenstock) or Transitions.RTM. (Trademark of Transitions Optical Inc.), which contained only spirooxazines as photochromic dyes. In the early 1990s, products such as Transitions.RTM. Plus (since 1992), Transitions Eurobraun.RTM. (since 1994) and Hoya Sunbrown.RTM. (since 1994) of the Hoya Lens Corporation or Rodenstock Perfalit Colormatic.RTM. neu (since 1995) reached the market, which already contained pyrans in addition to spirooxazines and/or fulgides. Newer products, such as Transitions.RTM. III, preferably use pyrans, especially naphthopyrans and larger ring systems derived from these.
In U.S. Pat. No. 4,818,096, compositions are described, which contain at least two photochromic compounds, one of the at least two photochromic compounds being a spirobenzopyran or spironaphthopyran, substituted in the 2 spiro position with an adamantyle group, and the other a benzopyran or naphthopyran, substituted with a nitrogen-containing group in the 2 position of the pyran ring. However, these compositions exhibit, on the one hand, unsatisfactory decolorization rates and, on the other, owing to the fact that the compounds are present to some extent (about 10 to 20%) in the open form, an inherent color, which interferes with the intended use.
In U.S. Pat. No. 5,753,146, compositions are described, which contain at least two photochromic naphthopyran compounds, especially 3[H]-naphtho[2,1-b]-pyran and 2[H]-naphtho[1,2-b]pyran. However, these naphthopyran compounds do not have any amino-substituted aryl groups, which are linked to the carbon atom adjacent to the oxygen atom of the pyran ring. With mixtures like those described in U.S. Pat. No. 5,753,146, gray or brown glasses, which are relatively color neutral, can be produced. One of the main problems of such glasses is, however, the rapid aging, which becomes noticeable, on the one hand, by a decreasing darkening and, on the other, by a yellowing.
Even mixtures of antioxidants, UV absorbers and hindered amines as light stabilizers, which have only been ascertained in protracted series of experiments, are able to mitigate the aforementioned problem with respect to a rapid aging only inadequately. This is also indicated in the recently published U.S. Pat. No. 5,770,115, in which a composition, comprising (a) 5 to 50% by weight of at least one polyphenol antioxidant, (b) 5 to 50% by weight of an organic UV absorber and (c) 10 to 90% by weight of at least one hindered amine light stabilizer, based on the total amount of stabilizer, is described, the ratio by weight of naphthopyran to stabilizer being 2.5:1 to 1.5:1. Even the best of these mixtures at the very least still doubles the original b* value in the a*-b* color space of the CIELAB color system and has a performance loss of at least 20% in the course of the aging test.
Moreover, migration of almost all of the additives used occurs upon warming. When eyeglass lenses are coated, this can lead to defects, such as layer detachment. This is frequently the case, particularly when there is photochromic surface coloration.
Further disadvantages of the compositions, available in the state of the art, lie therein that, without exception, the color, perceived for plastic objects in the form of glasses, is not neutral, since the spectral absorption in the range from 400 to 650 nm does not have a constant value. Moreover, for corresponding applications, the long wave absorption must usually also fulfill certain requirements. Certain glasses, when darkened to an extreme extent by intensive UV radiation, for example, when (glacier) skiing, exhibit the unpleasant property of color distortion. This is due to the fact that the eye, with this darkening, receives very much more information from the wavelength region above 650 nm than from the region below 650 nm; therefore, for example, snow appears to be tinted red.